Today people demand connectivity to services from all over the world without leaving their homes. They want video on demand, Internet access, live on-line gaming, and access to the world market place from the comfort of their living room. In order to support these ideas and requests a cable industry group developed the Data Over Cable Service Interface Specification (DOCSIS). DOCSIS defines a procedure for transferring digital information through the existing cable television infrastructure.
DOCSIS specifies downstream traffic transfer rates between 27 and 36 mega bits per second (Mbps) over a radio frequency (RF) path in the 50 mega hertz (MHz) to 750+ MHz range, and upstream traffic transfer rates between 320 kilo bits per second (Kbps) and 10 Mbps over a RF path between 5 and 42 MHz. But, because data over cable travels on a shared loop, individuals will see transfer rates drop as more users gain access. New proposals for the DOCSIS 3.0 specification may support transfer rates up to 160 Mbps in the downstream direction and 120 Mbps in the upstream direction in order to extend the useful life of the cable television (CATV) infrastructure.
In order to facilitate these transfer rates, the condition of the cable structure and its proper termination is critical. Many signal processing techniques, Time Division Multiple Access (TDMA), Quadrature Amplitude Modulation (QAM), Quadrature Phase Shift Keying (QPSK), Trellis Coded Modulation (TCM) and the like are used to extend the capabilities of the aging CATV structure.
A critical aspect of the DOCSIS operation requires maintaining the integrity of the cable structure itself. In order to maintain the operational integrity of the cable structure, sophisticated test and analysis equipment must be used to detect and resolve problems. By coupling specific test equipment to the cable test points, signals between the Cable Modem Termination System (CMTS) and the Cable Modem (CM) may be analyzed.
The downstream path, from the CMTS to the CM, is critical to analyze because the CMTS manages the transmission of data content into the cable structure. Power and phase of the transmission signals have already been adjusted to compensate for losses prior to the CMTS. In the structure beyond the CMTS there may be many branches or CM attach points that can affect the signal quality. Each node in the cable structure may require different signal processing and amplification in order to deliver good data to the end user. The analysis of the delivery path is crucial to the efficient delivery of transmitted data. A network monitor may capture and examine the signal for abnormalities in amplitude, phase, or modulation, but is limited to active device analysis.
In order to analyze the downstream path, from the CMTS to the CM, the test equipment must perform the testing without disrupting the active flow of data to the CMs. The DOCSIS protocol provides for a device to become connected and recognized on the network on a first available channel basis. If a device had previously been active on the network, the protocol attempts to re-attach the device on the same channel that previously provided a satisfactory transfer.
The tendency of the DOCSIS protocol to restore a device to the last known working channel makes it difficult for a test device to verify more than a single channel that isn't actively transferring data to an end user's CM. The current methodology actively monitors the data traffic on subscribed channels, without any proactive testing of the available unused channels in the network.
Thus, a need still remains for a test system with user selectable channels for simplifying the analysis of the downstream path in the cable structure. In view of the overwhelming popularity high-speed content delivered to the home, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to save costs, improve efficiencies and performance, and meet competitive pressures, adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.